Epidemiological transitions and the changing face of medical geology.

Medical geology is defined as the study of the relationship between the geosphere and human health. Two recent books in this rapidly expanding field (1, 2) focus on current issues that generally involve exposure to toxic elements or compounds of direct geogenic origin, such as arsenic, mercury, and asbestos. A detailed understanding of these issues ultimately leads to scientifically based recommendations for public health interventions that decrease human morbidity and mortality. However, the relationship between our geological environment and our health antedates current public health practice by at least 200 000 years, when the first modern humans appeared. Since that emergence of Homo sapiens in Africa, our species has undergone three epidemiological transitions, major changes in the pattern of our disease burden that result from steps in cultural evolution. Thus the advents of agriculture, industrialization, and globalization have led to the emergence of new diseases as well to the disappearance of others. It is the aim of this paper to trace the changing role of medical geology through these epidemiological transitions, thereby providing, for the first time, a historical perspective on the importance of this field.